Has Earth's Missing Heat Been Found? Page 2

Surface currents that form a portion of the Atlantic Meridional Overturning Circulation.

Woods Hole Oceanographic Institution

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GlobalWarmingRightBeforeYourEyes:Photos

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The effects of global warming are frequently projected decades into the future, but two recent reports -- one from the U.S. Global Change Research Program and the other from the U.N. -- put into sharp focus visible consequences of our warming planet.
An increase in temperature, extreme weather, loss of ice and rising sea level are just a few of changes we can measure right now. Let's take a look at some of the most concerning trends.
BLOG: War Of The Words: Climate Change Or Global Warming?

John Hyde/Design Pics/Corbis

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Glaciers are shrinking worldwide and permafrost is thawing in high-latitude and high-elevation areas, reports this year's Fifth Assessment Report from the Intergovernmental Panel on Climate Change.
BLOG: Dire Outlook For Climate Impacts, New Report Says

Eric Meola/Corbis

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Only a few extinctions are attributed to climate change, reports the IPCC, but climate change that occurred much more slowly, over millions of years, caused major ecosystem shifts and species extinctions.
Land and sea animals are changing their geographic ranges and migratory patterns due to climate change.
NEWS: Climate Change: Why Haven't We Done More?

Nick Garbutt

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Sea level around the world has increased by about 8 inches since 1880, reports the 2014 National Climate Assessment, which projects a 1 to 4 foot rise by the end of the century.
PHOTOS: Craziest Environmental Ideas (That Could Work)

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Excess CO2 is dissolving in the ocean and decreasing the pH of seawater. The ocean is about 30 percent more acidic than it was in pre-industrial times.
More acidity in the oceans makes it harder for animals to form calcium carbonate shells and skeletons and erodes coral reefs.
11 Health Threats from Climate Change

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The probability of a Sandy-like storm deluging New York, New Jersey and other parts of the East Coast has nearly doubled compared to 1950, according to the American Meteorological Society. Even weaker storms will be more damaging now than they were 10 years ago because of rising sea levels.
Superstorm Sandy cost the nation $65 billion, according to the 2014 National Climate Assessment, and 2012's Hurricane Isaac cost $2.3 billion.

Andrew Lichtenstein/Corbis

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The global sea level rises along with the temperature for two major reasons. For one, heat causes water to expand, which causes the existing water to take up more space and encroach on the coast. At the same time, ice at the poles and in glaciers melts and increases the amount of water in the oceans.
PHOTOS: Melting Glaciers

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Across the United States, heavy downpours are on the rise, especially in the Northeast and Midwest. Increases in extreme precipitation are expected for all U.S. regions, reports the 2014 National Climate Assessment.
NEWS: Shrinking Greenland Glacier Smashes Speed Record

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The most recent IPCC report states with "very high confidence" that current climate-related extremes like heat waves, droughts, floods, cyclones and wildfires are showing that countries around the world, at all development levels, are significantly unprepared.
The American Meteorological Society estimates that approximately 35 percent of the extreme heat in the eastern United States between March and May 2012 resulted from human activities' effects on climate. The AMS warned that deadly heat waves will become four times more likely in the north-central and northeastern United States as the planet continues to warm.
NASA: Global Warming Goes On

Tung and Chen noticed that the North Atlantic's heat content (a measure of stored energy) shifted in 1999, about when the hiatus began. The ocean started absorbing heat at depths below 984 feet (300 m). (The South Atlantic Ocean also took up some heat.) These regions stored more heat energy than the rest of the world's oceans combined, even the enormous Pacific Ocean, the researchers' temperature data show.

Over the next 200 years, the ocean is expected to rise 10 feet, putting many major cities worldwide underwater.

DCI

So how does the Atlantic cool an entire planet? The likely culprit is a natural climate cycle linked to the Atlantic Meridional Overturning Circulation (AMOC) current, Tung said. The AMOC is part of a worldwide ocean conveyor belt. Here's how the AMOC works: In the North Atlantic, salty tropical water flowing north cools off and sinks. This water, dense because it is cool and salty, heads south toward the equator, then eventually rises again in the South Atlantic. When the water sinks, it traps heat in the ocean depths. Ocean surface temperatures drive the current: fast when cold, slow when warm. [Images: The World's Biggest Oceans and Seas]

Between 1945 and 1975, the cycle was in a cool phase, sucking up atmospheric heat at a rapid pace. Toward the end of this cycle, in the 1970s, scientists noticed a suspected "global cooling" that was touted as the beginning of a possible Ice Age. But then the AMOC flipped to warming, corresponding to the rapid uptick in global temperatures. Finally, in 1999, the current switched back to a cold, speedy plunge into the ocean depths, taking extra heat along with it.

Such natural cycles make global warming look more like a staircase than a steady rise in temperatures, Tung said. "Right now, we're on the flat part of the staircase. We still have a few more years of the hiatus."

However, others scientists remain convinced the Pacific plays an important role in the global warming hiatus. Several recent studies affirm the link between the pause and the changes in the Pacific. An Aug. 3 study in the journal Nature Climate Change found that faster trade winds over the Pacific bring up cold water and cool the atmosphere. An Aug. 17 study, also in Nature Climate Change, suggested the Pacific Decadal Oscillation climate cycle might be responsible for the hiatus. That cycle flips every 20 to 30 years.

"I still think the Pacific Ocean is playing the lead role in this ocean heat uptake, but this study is important as it points to an additional role from the Atlantic and Southern Oceans," said England, who co-authored the Aug. 3 Nature Climate Change study.